The present invention relates to steerable catheters which are particularly useful in direct myocardial revascularization procedures.
Direct myocardial revascularization (DMR), also referred to as percutaneous myocardial revascularization, is a technique that allows physicians to treat patients who have sustained a myocardial infraction by burning channels in the myocardium that has been determined to be ischemic heart tissue. The channels, which are burned by a laser, allow for angiogenesis, i.e., the formation of blood vessels.
Several myocardial revascularization procedures are known that require that the chest wall be opened to access the heart muscle with laser devices. The procedures are not very desirable, as they require major surgery that can result in severe complications. Aita et al., U.S. Pat. No. 5,389,096, describes a procedure for performing myocardial revascularization percutaneously by inserting a guidable elongated flexible lasing apparatus, such as a catheter, into a patient""s vasculature. The distal end of the catheter is guided to an area in the heart to be revascularized. The inner wall of the heart is then irradiated with laser energy to cause a channel to be formed from the endocardium into the myocardium.
For obvious reasons, DMR catheters require the physician to have more control and information than other catheters having an optic fiber, such as ablation catheters. Aita et al. generally describes a DMR catheter. The present invention is directed to an improved DMR catheter which allows the physician to have greater control and obtain more information than the catheter described in Aita el al.
The present invention provides a steerable catheter particularly useful in DMR procedures used to treat ischemic heart tissue. The steerable DMR catheter comprises a catheter body or shaft, a tip section attached to the distal end of the catheter body and a control handle attached to the proximal end of the catheter body. A puller wire is anchored at its proximal end in the control handle and extends through a lumen in the catheter body and a lumen in the tip section and is anchored at or about the distal end of the tip section. Manipulation of the control handle results in deflection of the tip section. An optic fiber suitable for transmission of laser energy extends through the control handle, catheter body and tip section, the distal end of the optic fiber being generally flush with the distal end surface of the tip section. The proximal end of the optic fiber extends proximally from the control handle to a suitable connector which connects the optic fiber to a source of laser energy. The optic fiber is used to transmit laser energy for creating channels, i.e. blind holes, in the heart tissue which induces revascularization.
In a preferred embodiment of the invention, the tip section of the DMR catheter comprises an electromagnetic sensor. The electromagnetic sensor is connected to a circuit board by means of a sensor cable which extends proximally through the tip section, catheter body, and control handle. The circuit board is preferably housed in the handle. Signals from the circuit board are transmitted through a cable to a computer and monitor. The electromagnetic sensor allows a physician to create a visual representation of the heart chamber and to view the location of the sensor, and therefore the catheter tip, within the chamber.
In another preferred embodiment, the DMR catheter comprises a tip electrode and one or more ring electrodes spaced proximally from the tip electrode. Each electrode is connected by means of electrode lead wires which extend through the tip section, catheter body and control handle to an appropriate connector, and from there, to a suitable monitor. The tip and ring electrodes allow the electrical activity of the heart tissue to be mapped. In a particularly preferred embodiment of the invention, the DMR catheter comprises both an electromagnetic sensor within the tip section and a tip electrode and one or more ring electrodes. This combination allows a physician to map the electrical activity of the heart wall of a particular chamber, e.g., the left ventricle, by means of the tip and ring electrodes to determine ischemic areas and simultaneously to record the precise location of the tip section within the heart by means of the electromagnetic sensor to create a three-dimensional representation of the heart chamber which is displayed visually on a monitor. Once an ischemic area has been mapped, the tip section is moved to that area and deflected to allow the optic fiber to be generally normal to the heart wall, and then laser energy is transmitted onto the heart tissue for creating a channel within the heart tissue.
In another aspect of the invention, the optic fiber comprises a protective jacket, preferably made out of aluminum. The optic fiber extends through the control handle and catheter body and into the tip section which carries a tip electrode. In the tip section, the optic fiber extends through an optic fiber lumen in the tip electrode, the distal end of the optic fiber being flush with the distal face of the tip electrode. The aluminum jacket is removed from the distal portion of the optic fiber which extends through the tip electrode. This removal avoids the possibility that particles of the aluminum jacket may break free into the heart, especially during laser transmission, which could result in a stroke. This removal also prevents the possibility of an electrical short between the aluminum jacket and the tip electrode, which could result in the patient receiving a lethally high voltage during laser transmission.
In another aspect of the invention, there is provided a DMR catheter having an infusion tube which extends from the proximal end of the catheter body through a lumen in the catheter body and into the tip section. The distal end of the infusion tube is open at the distal end of the tip section at a position adjacent the optic fiber so that fluids, including drugs to induce angiogenesis, may be passed through the catheter to the heart tissue. In a preferred embodiment, the DMR catheter comprises an infusion tube and a tip electrode having an infusion passage adjacent the optic fiber lumen. The infusion tube is connected to, preferably inserted into, the infusion passage in the tip electrode so that fluids passing through the infusion tube will enter and pass through the infusion passage in the tip electrode and to the heart tissue. The proximal end of the infusion tube terminates in a luer hub or the like.
In yet another aspect of the invention, the catheter body or shaft comprises a construction which exhibits improved torsional stability, resulting in improved tip control while minimizing wall thickness. The catheter body comprises a single central lumen and is formed by a tubular outer wall of polyurethane or nylon with a braided stainless steel mesh imbedded in the outer wall. The inner surface of the outer wall is lined with a stiffening tube, preferably made of polyimide or the like. The use of a polyimide stiffening tube provides improved torsional stability while at the same time minimizing the wall thickness of the catheter. This, in turn, maximizes the diameter of the central lumen. Such a construction is particularly useful in steerable DMR catheters in which an optic fiber, a puller wire, electrode leads, and an electromagnetic sensor cable all extend through the lumen of the catheter body, but is also useful in other steerable catheter constructions.
A preferred construction of the DMR catheter also includes a tubular spacer, between the polyimide stiffening tube and the tip section. The spacer is made of a material less stiff than the material of the stiffening tube, e.g., polyimide, but more stiff than the material of the tip section, e.g., polyurethane. Teflon(copyright) is the presently preferred material of the spacer.
In a preferred method for constructing the catheter, the stiffening tube is inserted into the tubular outer wall until the distal end of the stiffening tube butts against the tubular spacer. Force is applied to the proximal end of the stiffening tube which tube is then fixed in position, e.g., by glue, to the outer wall. The application of force on the proximal end of the stiffening tube assures that no gaps will form between the stiffening tube and tubular spacer or between the spacer and tip section as a result of repeated tip deflection.
In a steerable catheter construction comprising a stiffening tube and spacer, a puller wire preferably extends through a non-compressible compression coil which is fixed at its proximal end to the proximal end of the catheter body by means of a glue joint and fixed at its distal end to the proximal end of the tip section at a location distal to the spacer by means of a second glue joint. This arrangement prevents compression of the spacer during tip deflection which, in turn, permits the use of a thin walled spacer.
In yet another aspect to the invention, a control handle is provided which can be manipulated to deflect the tip section of the catheter. The control handle has a first member which is attached to the catheter body and a second member movable with respect to the first member, which is attached to the puller wire. In this arrangement, movement of the first member relative to the second member results in deflection of the tip. The handle comprises a guide tube through which the optic fiber extends. The guide tube is fixedly secured to the first or second member. Within this guide, the optic fiber is afforded lengthwise movement with respect to both the first and second members.